(a) Field of the Invention
The invention relates to a multi-domain liquid crystal display, particular to a multi-domain liquid crystal display where fringe fields are produced by means of a polarity inversion control.
(b) Description of the Related Art
Typically, the display contrast and response speed offered by a VA (vertically-aligned) mode liquid crystal display, which uses a negative liquid crystal material and vertical alignment film, are better compared with a TN (twisted-nematic) mode LCD, since liquid crystal molecules are aligned in a vertical direction when no voltage is applied. Also, it is known the viewing angle performance of a VA mode LCD is improved by setting the orientation directions of the liquid crystal molecules inside pixels to a plurality of mutually different directions; that is, forming multiple independent domains in the liquid crystal display.
FIG. 1A shows a schematic diagram illustrating a conventional design of a multi-domain vertically-aligned liquid crystal display (MVA LCD). Referring to FIG. 1A, a top substrate 102 and a bottom substrate 104 are both provided with protrusions 106 having different inclined surfaces and covered by vertical alignment films 108. Hence, the liquid crystal molecules near the inclined surfaces orientate vertically to the inclined surfaces to have different degrees of pre-tilt angles. In case the pre-tilt liquid crystal molecules exist, surrounding liquid crystal molecules are tilted in the directions of the pre-tilt liquid crystal molecules when a voltage is applied. Thus, multiple domains each having individual orientation direction of liquid crystal molecules are formed. Besides, the domain-regulating structure for providing inclined surfaces includes, but is not limited to, the protrusions 106, and other structure such as a concavity structure 114 shown in FIG. 1B may also be used.
However, when one compares the transmission path of light I1 and that of light I2 shown both in FIGS. 1A and 1B, it is clearly found the pre-tilt liquid crystal molecules through which the light I2 passes under a field-off state may result in surplus phase differences (.nd.0) to cause light leakage. Accordingly, additional compensation films must be provided to eliminate the light leakage.
FIG. 2 shows a schematic diagram illustrating another conventional design of a MVA LCD. Referring to FIG. 2, the transparent electrode 204 on the substrate 202 is provided with openings 206. Due to the fringe fields at the edges of transparent electrode 204 and at each opening 206, the liquid crystal molecules are tilted toward the center of each opening 206 to result in a multi-domain LCD cell. However, the strength of the fringe fields generated by the formation of the openings 206 is often insufficient, particularly when the widths and the intervals of the openings 206 are not optimized. Besides, since the azimuth in which the liquid crystal molecules tilt due to fringe fields includes all directions of 360 degrees, a disclination region 210 often appears beyond the openings 206 or between two adjacent openings to result in a reduced light transmittance.